Brake booster with compression spring extension limiting links

Abstract

The invention relates to a vacuum-operated servo-brake comprising, in a casing consisting of a shell (10) and a cover (12), a piston (20) separating leaktightly two inner chambers (22, 24), a valve means controlled by a rod (32) projecting from the casing in order to ensure the operation of the servo-brake, and a prestressed spring (34) for returning the piston (20) to its rest position substantially abutting the cover (12), the spring (34) bearing on the shell (10). According to the invention, the spring (34) comprises a mechanism enabling its extension to be limited when the shell (10) and the cover (12) are not fixed to each other.

We claim: 
     
       1. A vacuum-operated servo-brake comprising, in a casing comprising a shell and a cover, a piston separating leaktightly two inner cambers, valve means controlled by a rod projecting from said casing for operation of said servo-brake, and a prestressed spring for returning said piston to a rest position substantially abutting said cover, said spring bearing on said shell and comprising means for limiting extension of the spring when said shell and cover are not connected with each other, said limiting means comprising a first collar located between said shell and an end of said spring adjacent said shell, and a plurality of links of predetermined maximum length connecting said collar with said piston, said links articulated so as to move away from said spring when the spring is compressed. 
     
     
       2. The vacuum-operated servo-brake according to claim 1, wherein said limiting means comprises a second collar located between said piston and an end of the spring adjacent said piston, said links connecting said collars to one another. 
     
     
       3. The vacuum operated servo-brake according to claim 2, wherein said links each comprise a first strand-part one end of which is fixed to said first collar and a second strand-part one end of which is fixed to one of said piston and said second collar, an aperture located at the other end of one of said first and second strand-parts and the other end of the other of said first and second parts having a protuberance, the other of said first and second strand-parts sliding freely in said aperture until halted by interaction of said protuberance and the other end of the one of said first and second strand-parts.